Multiple sclerosis (MS) is a common chronic neurological disorder affecting approximately 1 in 1000 Caucasians, particularly persons of Northern European origin who reside in temperate climates. Although there is still no cure for MS, several drugs can delay the progression of clinical worsening of patients with relapsing-remitting MS (RRMS). However, no treatment is available for primary and secondary progressive MS (PPMS and SPMS). For more than 10 years, we have focused our research on the role of CD24 in MS. Our studies in animal models established that the primary function of CD24 is to regulate the persistence of autoreactive T cells after they have reached the CNS. The significance of this checkpoint for MS is supported by genetic studies that demonstrate that a polymorphism of CD24 controls risk and/or progression of MS. Based on these novel observations, we have devoted more than 10 years of effort to develop therapeutics that target CD24 for the treatment of MS. We have completed manufacture, efficacy, and toxicity studies in animal models of EAE and in non-human primates. We have recently received FDA approval of our IND for a first-in- human study. Here we propose a randomized, double-blind, placebo-controlled, single ascending dose study to assess the safety, tolerability, immunogenicity and pharmacokinetics of CD24Fc in healthy adult subjects. The phase I studies will be carried out by one of the most respected CROs in the nation with strong track record in clinical drug testing. The phase I studies proposed herein will provide crucial safety information for a go-no-go decision of the phase II studies. The human PK and immunogenicity data will be valuable for the design of phase II studies.